Lower Mekong basin W18 W18 Threatened species HE plains of the lower Mekong still retain some areas of near- Tprimary habitat, with mosaics of open deciduous dipterocarp CR EN VU Total forest, seasonally inundated wetlands and grasslands, and riverine 42410 habitats. The region supports the entire world population of Giant Ibis, together with a high proportion of the global population of ———— White-shouldered Ibis and large numbers of several other threatened —— 11 birds. The swamp forests around Tonle Sap, the world’s largest floodplain lake, have the most important waterbird colonies Total 42511 remaining in mainland South-East Asia, with globally significant breeding populations of Spot-billed Pelican, Lesser Adjutant and Key: = breeding in this wetland region. = passage migrant. Greater Adjutant. The seasonally inundated grasslands around the = non-breeding visitor. lake are probably the global stronghold for Bengal Florican, and The Lower Mekong basin region is within grasslands in the Mekong floodplain and delta support several Conservation International’s Indo-Burma Hotspot hundred pairs of Sarus Crane. In addition to the waterbirds, this (see pp.20–21). region has important populations of White-rumped and Slender- billed Vultures (particularly given their rapid declines in South Asia: see G03) and several threatened birds found in forests and associated wetlands (White-winged Duck, Masked Finfoot and Green Peafowl: see F06). ■ Key habitats Freshwater wetlands on riverine plains, seasonally inundated grassland, open deciduous forest, swamp forest. ■ Countries and territories Laos; Cambodia; Vietnam. The Mekong flood-plain was originally a mosaic of open forest, small seasonal pools and wet grasslands. PHOTO: ELEANOR BRIGGS 221 Lower Mekong basin W18 Tibetan plateau Tibetan Table 1. Outstanding Important Bird Areas in the lower Mekong basin. IBA name Status Territory Threatened species 1 Xe Kong plainsF06 (PA) Laos Lesser Adjutant, White-shouldered Ibis, Giant Ibis and Sarus Crane occur in small numbers 2 Dong KhanthungF06 — Laos Large population of Lesser Adjutant, small numbers of Giant Ibis, Sarus Crane and Manchurian Reed-warbler 3 Western Siem PangF06 — Cambodia Lesser Adjutant, White-shouldered Ibis, Giant Ibis, Sarus Crane and White-rumped Vulture 4 ChhepF06 (PA) Cambodia A stronghold for Giant Ibis, also Lesser Adjutant, Greater Adjutant, White-rumped and Slender-billed Vultures, Sarus Crane and Manchurian Reed-warbler 5 LomphatF06 (PA) Cambodia Important for Lesser Adjutant, White-rumped and Slender-billed Vultures and Sarus Crane, also White- shouldered Ibis, Giant Ibis and Greater Adjutant 6 Upper Stung Sen catchmentF06 (PA) Cambodia Breeding Sarus Crane, also Lesser Adjutant, Greater Adjutant, White-shouldered Ibis and Giant Ibis 7 Ang Tropeang Thmor PA Cambodia Non-breeding Sarus Crane, also Spot-billed Pelican, Milky Stork, Lesser Adjutant, Greater Adjutant, White-shouldered Ibis and Bengal Florican 8 Preah Net Preah / Kra Lanh / Pourk — Cambodia Important for Bengal Florican, also Spot-billed Pelican and Sarus Crane 9 Prek ToalF06 PA BR Cambodia Most important site in mainland South-East Asia for breeding large waterbirds, including Spot-billed Pelican, Milky Stork, Lesser Adjutant and Greater Adjutant 10 Stung / Chi Kreng / Kampong Svay — Cambodia Important for Bengal Florican, also Lesser Adjutant, Sarus Crane and Manchurian Reed-warbler 11 Boeung Chhmar / Moat KhlaF06 (PA) BR,R Cambodia Large numbers of Spot-billed Pelican and Greater Adjutant, also Lesser Adjutant 12 Veal Srongae — BR Cambodia Large numbers of Lesser Adjutant, and Bengal Florican, also Greater Adjutant, White-shouldered Ibis and Manchurian Reed-warbler 13 Stung Sen / Santuk / Baray — BR Cambodia Large numbers of Bengal Florican and Manchurian Reed-warbler, also Milky Stork, Lesser Adjutant, Greater Adjutant, White-shouldered Ibis and Sarus Crane 14 Boeung Prek Lapouv — Cambodia Important non-breeding population of Sarus Crane, also Bengal Florican 15 Ha Tien plain — Vietnam Important non-breeding population of Sarus Crane, very small numbers of White-shouldered Ibis and Bengal Florican Some of the waterbirds of this region occur in IBAs listed for region F06, Yok Don NP (Lesser Adjutant, Giant Ibis and White-rumped Vulture) and Cat Tien NP (Lesser Adjutant and White-shouldered Ibis). Note that more IBAs in this region will be included in the Important Bird Areas in Asia, due to be published in early 2004. Key Status: PA = IBA is a protected area; (PA) = IBA partially protected; — = unprotected; BR = IBA is wholly or partially inside Tonle Sap Biosphere Reserve (see pp.34–35); R = IBA is wholly or partially a Ramsar Site (see pp.31–32); F06 = also supports threatened forest birds of region F06. 222 Lower Mekong basin OUTSTANDING IBAs FOR extensive areas of open deciduous forest studded with small THREATENED BIRDS (see Table 1) seasonal pools (trapaengs) and seasonally wet meadows W18 (veals), most notably on the plains of northern and eastern This region supports by far the largest waterbird Cambodia, which are the last stronghold for Giant Ibis and populations remaining in South-East Asia, and a total of breeding grounds for White-shouldered Ibis and Sarus fifteen IBAs have been selected, chiefly for their importance Crane. In comparison to the plains of Myanmar (W16) and to Spot-billed Pelican, Lesser Adjutant, Greater Adjutant, Thailand (W17), human population density in most of the White-shouldered Ibis, Giant Ibis, White-rumped Vulture, lower Mekong basin is low, but the region’s wetlands have Slender-billed Vulture and Bengal Florican. nevertheless been subject to professional hunting and seasonal subsistence fishing over a long period, and these CURRENT STATUS OF HABITATS AND pressures are growing. The Mekong and its tributaries THREATENED SPECIES support the only remaining examples of near-intact riverine habitats and bird communities in South-East Asia. The lower Mekong and its major feeder rivers, the Sesan, However, islands in these rivers are used increasingly by Sekong and Srepok, retain the most intact riverine itinerant fishermen and their families for camps, and there is floodplain habitats in the Asia region. There are still regular motorised boat traffic, which may account for the apparent extinction of the Mekong’s Indian Skimmer population. Various proposed hydropower schemes in the The large undeveloped tracts of flood-plain habitats in northern Mekong catchment threaten river flow rates and seasonal and eastern Cambodia are the last stronghold for Giant Ibis. water levels (see below). In Vietnam and parts of southern Cambodia, the Mekong floodplain and delta has been almost totally converted to rice paddy, while much of the remainder is intensively used. Large areas of mangrove and Melaleuca wetlands in the delta were destroyed during the Vietnam War, then replanted, but later cleared for aquaculture. The inundation zone of Tonle Sap lake still has extensive tracts of swamp forest, and grasslands which are subject to a complex and ancient Khmer agricultural ecology. The swamp forests support the only remaining large colonies of communally nesting waterbirds in South-East Asia, and the traditionally managed grasslands have a high proportion of the global population of Bengal Florican. CONSERVATION ISSUES AND STRATEGIC SOLUTIONS (summarised in Table 3) Habitat loss and degradation ■ CONVERSION TO AGRICULTURE Wetlands and grasslands in this region are threatened by the PHOTO: ALLAN MICHAUD PHOTO: large-scale intensification of agriculture, in particular the Table 2. Threatened birds of the lower Mekong basin. Species Distribution and population Spot-billed Pelican Pelecanus philippensis VU Large breeding population in the swamp forest around Tonle Sap lake Milky Stork Mycteria cinerea VU Very small numbers breed in the swamp forest around Tonle Sap lake Lesser Adjutant Leptoptilos javanicus VU Significant numbers breed at Tonle Sap lake, and at lower densities throughout the forested plains Greater Adjutant Leptoptilos dubius EN Significant numbers breed in the swamp forest around Tonle Sap lake White-shouldered Ibis Pseudibis davisoni CR Significant numbers breed in Cambodia; close to extinction in Laos and southern Vietnam Giant Ibis Thaumatibis gigantea CR Entire global population now confined to this region, mainly in northern and eastern Cambodia, but also very small numbers in adjacent parts of Laos and Vietnam White-rumped Vulture Gyps bengalensis ? CR Widely distributed on the plains, in deciduous forest and open habitats Slender-billed Vulture Gyps tenuirostris ? CR Widely distributed on the plains, in deciduous forest and open habitats Sarus Crane Grus antigone VU Several hundred pairs breed in northern Cambodia and southern Laos; outside breeding season moves to north-western and southern Cambodia and the upper Mekong delta in Vietnam Bengal Florican Houbaropsis bengalensis ? EN Significant population around Tonle Sap lake, dispersing to adjacent areas in the wet season; close to extinction in the Mekong delta in Vietnam Manchurian Reed-warbler Acrocephalus tangorum ? VU Recently found wintering in damp grasslands in Cambodia Other threatened waterbirds recorded from this region as rare (or perhaps extinct) visitors are: Black-faced Spoonbill Platalea minor, Pallas’s Fish-eagle Haliaeetus leucoryphus and Indian Skimmer Rynchops albicollis. In addition to the waterbirds, Greater Spotted Eagle Aquila clanga (VU; see F01) and Imperial Eagle A. heliaca (VU; see G01) occur in winter. Note that three species